This invention relates to a method of and device for reading an optical code such as a bar code and a two-dimensional code.
For using a camera containing an image sensor and set above a supply line to read out a very small optical code affixed to a work being transported thereon, various ideas have been developed for setting the timing for taking in an image. Japanese Patent Publication Tokkai 2000-293616, for example, disclosed a data code reader adapted to repeatedly take in images by means of a CCD camera at suitable time intervals after power is switched on and to switch to a decoding process based on the newest of the images already taken and stored in a memory device immediately after a trigger input is received.
According to this prior art technology, the timing for taking in images is completely asynchronous to the timing of the trigger input. Thus, there may be situations wherein the target optical code may not be in the image that has been obtained even if the trigger is generated as a trigger sensor (such as a fiber-type photoelectric sensor) detects the arrival of the position of a code on a work into the field of vision of the camera. There are situations where there are variations in the positioning of optical codes on a work. FIG. 19 shows an example wherein a two-dimensional optical code 8 is displaced from its intended position by ΔL. Thus, situations wherein the target optical code is not present in the field of vision of the camera or not completely present are not avoidable.